This invention relates to power transmission belts of the rubber type, particularly a belt whose back surface is adapted to make contact with an idler pulley, tensioner or other device tending to generate noise at the interface of such device with the belt.
Modern front end accessory drive systems for automobiles use serpentine multi-V-ribbed belts to link the engine crankshaft with various accessory driven pulleys. The backside of the belt typically impinges against backside idler pulleys and/or tensioning devices. Similarly, camshaft belt drive systems for automotive application systems use synchronous power transmission belts, the backsides of which are also trained about idler pulleys and/or tensioners. In addition, in many industrial belt drive applications, the drives include idlers or other devices against which the back of a multi-V-ribbed belt, synchronous belt, flat belt, V-belt or the like engages. In all of the foregoing automotive and industrial applications, chirping or “thumping” noise may be generated at the interface of the backside of the belt and drive device. The noise levels are often times unacceptable to the manufacturer or user.
For instance, overcords of belts of the multi-V-ribbed type typically employ a crosscord, or a bias laid fabric in which warp and weft yarns are oriented diagonally in respect to the longitudinal running direction of the belt, with an included angle between the yarns of about 90-120 degrees. These textile overcord reinforcements provide lateral stability, assist release of the belt slab from its mandrel during the manufacturing process, and allow tailoring the coefficient of friction on the backside of the belt. Typically these belts' overcord textile materials are calendared with gum rubber into the interstices (and on the faces) of the fabric and then the frictioned fabric/gum assembly is cut and respliced (using a Banner table-trademark) to provide the correct fabric cord orientation. This fabric cord orientation provides maximum or optimal lateral strength while allowing high flexibility in the longitudinal direction of the belt.
To effectively use these types of textile composite materials in the belt overcord, most manufacturing processes require making overlapping splices to reconnect the material after “Bannering”, as well as during the belt building process. These overlap splice joints create double thickness areas which have been found to cause noise and vibration in automotive serpentine drives. As the belt rotates around the drive, these splices contact the backside idlers, tensioners and the like which can cause the belt to chirp and the belt and drive components to vibrate.
With synchronous belt products it is common practice to use textile jackets which are made of stretch type fabrics, which are treated for adhesion, cut to length to match a particular belt length, and sewn or ultrasonically stitched back together to form a cylindrical tube or jacket for application to the belt teeth as a facing, or in the overcord. The resulting seams can serve as noise generators, and the overall process is time consuming and expensive.
The foregoing belt types also typically bear on their exterior belt back surface a label to identify the belt. A typical labeling process involves applying a polymeric film e.g. Mylar (Du Pont trademark) polyester, or other substrate transfer label against the belt sleeve in the course of its vulcanization. The Mylar label embeds into the outer rubber surface of the belt, and then the Mylar backing is stripped from the sleeve after conclusion of vulcanization, leaving a negative imprint, i.e. ridges or steps in the belt back surface which serve as additional noise generator sites.
The use of knit overcord fabrics, per se, is known from U.S. Pat. No. 3,981,206 (Miranti et al). However, in the belt construction of Miranti et al, the belt is built up on a cylindrical drum by applying various layers of material wrapped therearound, including the outer (nontubular) knit fabric. Such wrapping process will produce a seam or lapped joint, which will serve as a noise generator in backside idler and tensioner drives.
Seamless knitted tubular fabrics have also been used in the overcord of power transmission belts of the liquid cast (polyurethane) type. Unexamined Japanese patent application no. 7-243 483 (Bridgestone), published Sep. 19, 1995, discloses a multi-V-ribbed belt in which the tubular knit in the overcord is positioned directly against the tensile cord prior to liquid casting. The tensile cord and tubular knit make direct contact in the final fabricated liquid cast belt.
It is an object of this invention to overcome drawbacks in the prior art by providing a rubber power transmission belt utilizing a textile-reinforced overcord section which imparts lateral stability to the belt while allowing high flexibility in the running direction of the belt, and is characterized by an overcord free of joints, lapped splices or seams which would generate noise in belt drives using backside idlers, tensioners or the like.
It is a further object to achieve the foregoing without the need to Banner, calendar or otherwise prepare the outside jacket for the overcord of the belt, thus eliminating process steps and cost.